1. Field of the Invention
The present invention relates to ultraviolet curable materials and particularly to a unit for curing ultraviolet curable materials on both sides of a printed circuit board.
2. Related Prior Art
An increasing amount of materials are becoming available on the market which use ultraviolet light to achieve a tack-free cure. The advantage of these materials over their air or heat cured predecessors is speed of cure. Cure times of 2-24 hours were previously the norm for curing of coatings. Today, with ultraviolet curable materials, cure times of 2-10 seconds are commonplace.
Ultraviolet units are currently available which will cure a printed circuit board placed horizontally on a conveyor belt. The cure is only affected on the side which is exposed to the curing lamps leaving the other side of the printed circuit board unexposed. This makes it necessary to repeat the exposure cycle with the other side of the printed circuit board exposed to the ultraviolet source. This is acceptable when the material to be cured requires only a final cure to harden the material and is relatively tack-free to begin with (such as a soldermask). It is also acceptable if the material is to be applied one side at a time (as in spray coating). This horizontal conveyor system is, however, unacceptable in the event that a liquid coating, such as an ultraviolet curable conformal coating, is being applied by dip-coating or another coating method which coats both sides of the printed circuit board prior to curing. It is this application which requires an ultraviolet curing system which will simultaneously cure both sides of a printed circuit board without the need to place the printed circuit board on a conveyor belt.